3d cut pyramid letter
Something like this?




Make your letter(s), then extrude them with the text controls.
When it's about where you want it to be, do Object > Convert to > Mesh.
Now you can use a boolean modifier to cut it to the final shape.
Here's some information on the Boolean Modifier, if you need it: https://www.blender.org/manual/modeling/modifiers/generate/booleans.html